# Homework Help: Finding intervals of increasing, decreasing, concavity and inflection points

1. Nov 23, 2008

### ryan.1015

1. The problem statement, all variables and given/known data

let g(x)=2x^5-10x^3=15x-3. find the intervals on which G is increasing and decreasing. and find the intervals of concavity and the inflection points

2. Relevant equations

3. The attempt at a solution
i know how to find the increasing and decreasing intervals. i just cant figure out where the graphs cross the x axis. and the concavity intervals i cant figure out

2. Nov 23, 2008

### Staff: Mentor

Show us what you've done...

3. Nov 23, 2008

### ryan.1015

well i found the derivative to be 10x^4 +30x^2+15 but when i graphed it i couldt figure out where it crossed the x axis

4. Nov 23, 2008

### Staff: Mentor

Here's what you showed in your first post:
What's with that '=' right after the x^3 term? Did you mean that to be a '+'?

Assuming that's the case, g(x) = 2x^5 - 10x^3 + 15x -3
Your calculation for the derivative -- g'(x) is its name -- is incorrect.

5. Nov 24, 2008

### ElectroPhysics

I think from equating first derivative to zero u can easily find the point where no change occurs and beyond that it go on changing. and from 2nd derivative u can find the inflection points. Am I correct????

6. Nov 24, 2008

### Staff: Mentor

Equating the derivative to zero gives you the values where the tangent lines are horizontal, which can help you find local maxima and minima.